Digital cellular communication networks, e.g. the pan-European mobile communication network GSM for which technical specifications have been elaborated by the European Telecommunication Standards Institute ETSI, allow its users to initiate and receive calls at any geographical area within the radio coverage of the home public land mobile network HPLMN operated by the network operator selected by the subscriber and also within the radio coverage of partners of the network operator providing services within the home public land mobile network HPLMN, i.e. network operators having a roaming agreement with the HPLMN-network operator.
Basic sub-systems in the architecture of such a digital cellular communication network are a base station sub-system BSS, a network and switching sub-system NSS and an operational sub-system OSS. The base station sub-system BSS provides and manages transmission paths between mobile stations MS and the network and switching sub-system NSS. The network and switching sub-system NSS manages communications and connections to mobile stations MS.
FIG. 8 shows components of the digital cellular communication network being related Lo the network and switching sub-system NSS, the base station sub-system BSS and the mobile station MS, respectively.
To achieve a link between different service areas there is provided a gateway mobile service switching centre GMSC that serves to determine specific locations of a mobile station MS, to route calls towards a mobile station MS and to connect to other networks. The gateway mobile service switching centre GMSC is connected to a functional unit called home location register HLR wherein subscriber information and mobile information is stored to allow incoming calls to be routed to the mobile station MS.
To route a call to a mobile station MS the gateway mobile service switching centre GMSC is also connected to a mobile service switching centre MSC through which the mobile station MS can obtain a service. The mobile service switching centre MSC performs the necessary switching functions required for mobile stations MS covered by this mobile service switching centre MSC. Also, the mobile service switching centre MSC monitors the mobility of its mobile stations MS and manages necessary resources required to handle and update the location registration resources.
As shown in FIG. 8 the public land mobile network PLMN comprises a plurality of mobile service switching centres MSC and respective service areas each covering a predetermined number of basic cells wherein a mobile station MS can move. To this end, each mobile service switching centre MSC is connected to a visitor location register VLR. The visitor location register VLR is a functional unit that dynamically stores mobile station information, such as the location area in case the mobile station is located in the service area covered bay the visitor location register VLR. When a roaming mobile station MS enters a service area assigned to a specific mobile service switching centre MSC the mobile service switching centre MSC informs the associated visitor location register VLR.
Further, the base station sub-system BSS corresponds to physical equipment providing radio coverage to the above-mentioned cells which are approximately hexagonal geographical regions. Each base station sub-system BSS contains equipment required to communicate with the mobile station MS.
As shown in FIG. 9, there are three types of logical channels in the digital cellular communication network: traffic channel TCH, control channel CCH, and cell broadcast channel CBCH. The traffic channel TCH is used to transmit user information like speech or data. The control channel CCH is used to transmit control and signalling information. Finally, the cell broadcast channel CBCH is used to broadcast user information from a Mobile Services Switching Centre MSC to the Mobile Station MS listening in a given basic cell/basic service area.
In particular, each control channel CCH consists of a dedicated control channel DCCH used, e.g., for service request or subscriber authentication, a common control channel CCCH used for paging and access as well as a broadcast channel BCH. The broadcast channel BCH subdivides into a frequency control channel FCCH used to transmit frequency correction data, a synchronization control channel SCH including the TDMA frame number and the base station identity code BSIC required when measuring signal strength and finally a broadcast control channel ECCH.
Using this architecture for a digital cellular communication network, there may be provided different communication capabilities to subscribers. The basic communication services provided in the GSM digital cellular communication network are divided into three main groups: bearer services, teleservices, and supplementary services.
Contrary to digital cellular communication networks designed for mobile communication the World Wide Web, WWW, was initially designed as mechanism for document distribution, and now is rapidly becoming the standard infrastructure for diverse interactive applications. The ubiquity of the hypertext metaphor and browser technology make WWW applications attractive for a variety of business uses.
The WWW is based on a hypertext model where documents called Web sites or, equivalently, Web pages contain a plurality of different information, e.g. graphics, animation or music. The protocol underlying the WWW is the hypertext transmission protocol. This protocol is designed to support interactive WWW applications where, e.g., a WWW server responds to a request sent across a network by a WWW application or WWW client.
Within location dependent WWW services the geographical location of a user running a WWW application is conveyed from a mobile device, e.g., a laptop, to the relevant WWW server before requested location dependent information can be delivered by the WWW server.
In many instances the user must manually provide the geographical location, e.g., by connecting the mobile computing device to an ISDN socket. Of course this is very unwieldy, in particular when the user forgets to update the location or does not know how to specify the location.
Therefore, to make geographical location information available for applications running on a mobile device, satellite-based GPS systems have been proposed. Here links to mobile devices are established via so-called PCMCIA interfaces (Personal Computer Memory Card International Association) working with a hardware/software interface definition for portable computers. However, this approach requires additional GPS receivers to overcome the problem that most networks do not provide location specific information which is not very cost effective.
Another method for the exact geometrical positioning of mobile stations is proposed in EP-A-0 320 913. The mobile station receives signals from at least three fixed stations of known location and the location of the mobile station is then calculated on the basis of these signals. It is essential that all base station sub-systems are in precisely the same clock time. The mobile station information must be compiled to indicate propagation delay in receipt of timing reference signals from the base station sub-systems and then be transmitted thereto. Overall the method is complex and requires additional hardware and communication overhead.
Thus, currently the determination of the geographical position of a mobile station in a digital cellular communication network with low overhead and being simple to implement is not possible.
Also, services in a digital cellular communication network offering location dependent information, e.g. weather forecast or route traffic information etc., do not exist.